Copolymer compositions and method of preparation

ABSTRACT

Disclosed herein are novel copolymer compositions and method of preparing same that are useful for coating applications and as toners in the electrostatic printing industry. These copolymer compositions of the present invention are prepared by copolymerization of, on the one hand a low molecular weight unsaturated ester which is called a first monomer and on the other hand one or more copolymerizable long chain, C6 to C20 aliphatic ethylenically unsaturated monomers which is called a second monomer in a non-aqueous solvent, for example, isoparaffinic hydrocarbons.

United States Patent 91 Montillier I [4 1 Jan. 14,1975

COPOLYMER COMPOSITIONS AND METHOD OF PREPARATION 3,668,127 6/1972Machida et al. 252/621 L Primary ExaminerLewis T. Jacobs Attorney,Agent, or FirmWilliam D. Soltow, Jr.; Albert W. Scribner; Peter Vrahotes[57] ABSTRACT Disclosed herein are novel copolymer compositions andmethod of preparing same that are useful for coating applications and astoners in the electrostatic printing industry. These copolymercompositions of the present invention are prepared by copolymerizationof, on the one hand a low molecular weight unsaturated ester which iscalled a first monomer and on the other hand one or more copolymerizablelong chain, C to C aliphatic ethylenically unsaturated monomers which iscalled a second monomer in a non-aqueous solvent, for example,isoparaffinic hydrocarbons.

6 Claims, N0 Drawings BACKGROUND OF THE INVENTION This invention relatesto novel copolymer compositions, method of preparing same, non-aqueouscoating compositions and compositions in a non-aqueous system which areuseful as liquid toners for electrophotography. More particularly, thisinvention relates to copolymer compositions prepared by copolymerizationof low molecular weight esters such as vinyl esters and long chain, C toC aliphatic ethylenically unsaturated esters in an isoparaffinichydrocarbon solvent.

The use of liquid developers for electrophotography, i.e., renderingvisible as a permanent image a latent image consisting of a pattern ofelectrostatic charges, is well known. The use of liquid toners over thedry method of developing such a pattern of charges has advantages suchas, for example, sharper and better defined imagesimages having a higherdegree of economical use of the developer, a faster developing cycle,and simpler less expensive and more trouble free developing equipment.However, although the industry strongly desires an excellent liquidtoner, those which presently are available are subject to variousdeficiencies. For example, the liquid toners heretofore available havenot given sufficiently good resolution or sufficiently dense orsharpimages. In addition, with many liquid toners there has been aserious complaint that shelf life was not long enough in that some ofthe solids suspended within the liquid toner tended to settle andagglomerate too quickly making it necessary to redisperse them prior touse. This is especially true with respect to pigment containing liquidtoners.

In addition to the toner problems described above, conventionalelectrophotography has a disadvantage of giving copies which lack thefeel and look of plain bond paper and lack the contrast of offsetprinted material. However there is a trend today towards the developmentof so-called copier/duplicators which combine in one machine theadvantages of both electrophotography and offset printing. In suchmachines a lithographic plate is prepared by an electrophotographicprocess in which a photoconductor coated substrate is charged in thedark, exposed to an original image, toned with a socalled lithographictoner and subsequently chemically treated to render the image areasoleophilic and hydrophobic and the non-image areas hydrophilic andoleophobic as is normally done in any offset process. It is thereforepossible by the use of such copier/duplicator machines to generateoffset quality copies by an electrophotographic process.

The major requirement in such copier/duplicator machines is thelithographic toner that isto be used.

SUMMARY OF THE INVENTION The object of the present invention is toprovide novel copolymers compositions and a novel method of preparingsame.

A further object of the present invention is to provide a liquidelectrophotographic developer compositionwhich overcomes the aforesaiddeficiencies and drawbacks and which produces an improved developedelectrostatic image.

Another object of the present invention is to provide a liquidelectrophotographic developer composition that is free of pigmenttherein.

A further object of the present invention is to provide a novelelectrophotographic developer composition that is oleophilic andhydrophobic, has strong adhesion to photoconductive paper, excellentcharge holding characteristics, resistance to etching solutions,excellent fill-in capability and stability.

A liquid development process, for the development of latentelectrostatic images is disclosed by R. W. Gundlach in US. Pat. No.3,084,043. While a number of liquid development systems have beendisclosed many disadvantages have been present therein and these liquiddevelopment systems can be improved in many areas. Conventionalpigmented liquid development toners do not perform satisfactorily inoffset electrophotography because of lack of adhesion, poor stability,poor resistance to etching solutions, poor oleophilicity and lack ofacceptable fill-in ability.

The liquid toner composition of the present invention overcomes all ofthe above objections to the presently available liquid toners asdescribed above and may be utilized in both regular electrophotographythat is socalled Electrofax, or offset electrophotography. However, itmust be noted that the liquid toner of this invention is not limited inits use in offset electrophotography, and it can be used forelectrographic printing,.

' TABLE I Regular Electrophotography Offset Electrophotography Paper Nocolor requirement Paper can be heavily sensitized (high speed t W1.2-1.5 foot candle second) Paper must be white Limitation of the amountof sensitizing dyes (low speed' t I? 1.5-2.3 foot candle second) LiquidToner No need for pigments (toned paper is used as master forlithography) Good adhesion to substrate Must be based on black pigmentin order to obtain black and white copies Good adhesion to substra Goodstability Good stability Good charge holding Good charge holdingcharacteristics 2 characteristics No toxicity No toxicity Resistance toetching solutions Oleophilicity and hydrophobicity 1 V2: time ofexposure to a l,foot candle light source in order to decrease theacceptance voltage by half.

An additional advantage of the liquid development toner of the presentinvention is that it can be used in conjunction with zinc oxide as thephotoconductor. It is therefore a considerable saving and advantage tobe ableto produce copies of much superior quality to conventional Xeroxor Electrofax copies, by using the cheapest photoconductor (ZnO) incombination with the toner of this invention.

On the other hand, the use of conventional pigmented liquid developmenttoners have led to the obtaining of copies of poor quality ornon-acceptability and therefore would not be useful in offset printing.

Based on the requirements for an acceptable liquid development toner foroffset electrophotography, as described above, the toner based on thenovel copoly- In order to prepare the novel compositions'of the presentinvention, having allof the desirable characteristics as set forthabove, it has been found that nonaqueous dispersion of specificpolymeric materials in a suitable organic liquid carrier such as apetroleum fraction have said desired characteristics.

The organic liquid carrier is, as mentioned above, a petroleum fraction,it having been discovered that this particular class of carriers isuniquely capable of effecting the present invention by virtue of thefollowing attributes: (a) quick evaporation, e.g., a thin film of thecarrier will evaporate in a few seconds at a temperature below the charpoint of paper, so as to permit fast drying; (b) non-toxicity; low odor;(d) sufficient fluidity to allow the dispersed particles to migratetherethrough with ease so that they are capable of being quicklyelectrostatically attracted to and coupled with the pattern ofelectrostatic charges which is to be developed; (e) not attacking thebinder or other ingredients of the photoconductive coating on thelithographic master; (f) not bleeding the electrostatic charges beforethe particle is deposited so as to maintain any desired degree ofcontrast; and (g) inexpensiveness.

In order to obtain these beneficial attributes, the petroleum fraction,i.e., paraffinic solvent, should have an evaporation rate at least asfast as that of kerosene, but slower than that of hexane. Thereby, theevaporation of the liquid from a film will be rapid, e.g., two seconds,or less, at a temperature slightly below the char point of paper, itbeing customary to raise the temperature, of the film of liquiddeveloper to this level for thepurpose of evaporating the developerafter the electroscopic particles of the toner have been deposited byattraction on the electrostatically charged pattern. The petroleumfraction should have a low K.B. (Kauri-butanol) number, to wit, lessthan 30, and preferably between 25 and 30. This low K.B. numberminimizes the possibility that the petroleum fraction will attack thecoating binder, e.g., the binder for the zincoxide, or will attack ordissolve the dispersed copolymer particles of the toner. The petroleumfraction also should be substantially free of aromatic liquidconstituents, i.e., it should be substantially aromatic-liquid-free.This term as used herein, connotes that the proportion of aromaticliquids in the organic liquid carrier should not be in excess of twopercent by weight. The aromatic liquids have a strong tendency to attackthe coating binders, e.g. the coating binders for zinc oxide, but inconcentrations of less than two percent this tendency is so negligibleas to be unnoticeable. The petroleum fraction must have a highelectrical resistivity, e.g., in the order of at least ohm centimeters,and a dielectric constant of less than 3.5 so that the liquid carrierwill not dissipate the pattern of electrostatic charges which are to bedeveloped. The TCC (Tagliabue closed cup) flash point of the liquidcarrier should be at least 100F (38C) whereby under the conditions ofuse the liquid is considered non-flammable. The paraffinic solvent alsois non-toxic. it possesses no objectionable odor and preferably isodor-free, this being denoted by the term low odor.Consonant with itslow dielectric constant and high resistivity, the liquid carrier isnon-polar. The petroleum fractions have two other advantages of lowviscosity and inexpensiveness.

Examples of petroleum fraction organicliquid carriers having physicalcharacteristics which fall within the foregoing criteria are lsopar Gmanufacturedby Exxon Corporation and Soltrol 100 manufactured byPhillips Petroleum.

The monomeric materials to be dispersion copolymerized in the aliphatichydrocarbon solvent according to the present invention are, on one hand,as a so-called first monomer, a low molecular weight unsaturated estersuch as vinyl acetate and on the other hand or socalled second monomer,one or more long chain C to C aliphatic ethylenically unsaturated estersuch as lauryl methacrylate. Additional low molecular weight monomersthat may be employed in the composition and process of the presentinvention are vinyl esters such as vinyl acetate, vinyl propionate,esters of acrylic or methacrylic acid such as methyl, ethyl, propylesters of acrylic or methacrylic acids.

Examples of long chain monomers are long chain esters of acrylic, ormethacrylic acid, e.g., stearyl, lauryl, octyl, 2-ethyl hexyl and hexylesters of acrylic or methacrylic acid; and vinyl esters of long chainacids, e.g., vinyl laurate, vinyl stearate.

Any polymerization pressure can be employed in the processes of thepresent invention. Thus, pressures from atmospheric to 1000 psi orhigher can be em-- 'ployed. Atmospheric pressure is, of course,preferred. The polymerization temperature is chosen as a function of thecatalyst used and can vary between 60C and 150C, but will preferably bebetween .-l00C in order to avoid decomposition or degradation of thedispersed polymer.

The selection of the desired catalyst is merely a matter of choice. Anysuitable polymerization catalyst may be used such as the organicperoxides, the one found most preferable being benzoyl peroxide.

The reaction time should be sufficient to produce the copolymericmaterial within the desired molecular weight range which is between80,000 and 500,000. Typically reaction times will vary from a few hoursat 120C to one day at 80C.

The proportion of the first monomer to the second monomer to form thecopolymer dispersion in the aliphatic hydrocarbon solvent can vary overa wide range but generally from about 95 to 5 percent to 50 to 50percent by weight and preferably from to 10 percent to about 70 to 30percent by weight. The selection of the proportion will depend on thedesired end use of the novel composition of the present invention. Forexample, in lithographic applications the desired range of proportionswould be from about to 5 percent to about 75 to 25 percent by weightwhereas for coating applications the proportion range would be fromabout 25 to 75 percent to 95 to 5 percent byweight.

One of the more advantageous features of the compositions and process ofthe present invention is that there is no need for a pre-synthesizeddispersing agent such as those described in US. Pat. Nos. 3,095,388;

3,701,747 and 3,702,836. This reduces the cost and the time necessary toproduce the compositions of the present invention.

The preferred process for obtaining the copolymer dispersion of thepresent invention is by controlled dispersion copolymerization in whichthe first monomer to be dispersion copolymerized, preferably vinylacetate, is mixed with one or more monomers which will have the abilityto enhance the solvation of the main polymer in the solvent system,preferably lauryl methacrylate, at a vinyl acetate-lauryl methacrylateratio of about 80 to in an aliphatic hydrocarbon, preferably lsopar G,at a temperature of about 85C for a period of about six hours atatmospheric pressure.

The reaction product of the dispersion copolymerization of vinyl acetateand lauryl methacrylate comprises the copolymer and the aliphatichydrocarbon solvent and can be used directly as a coating composition oras a toner for offset electrophotography. It should be noted thatalthough not necessary, additives such as driers and coloring pigmentsin coating applications may be added and charge directors and pigmentsto give coloration may be added in the lithographic applications.

While it is not necessary with the electrostatic liquid tonercomposition of the present invention it might be desirable, forincreased contrast, to include in the toner composition a surfaceactive. agent also known as a charge director.

The charge directors, which are per se well known in the field ofelectrophotographic liquid toners, must be soluble or dispersible in theparaffmic solvent and must create or augment an'electrostatic charge onthe submicron dispersed particles. Examples of usable charge directorspursuant to this invention are aluminum stearate; cobalt salt of 2-ethylhexanoic acid; iron salt of 2- ethyl hexanoic acid; manganese salt of2-ethyl hexanoic acid; zirconium'salt of 2-ethyl hexanoic acid;manganese linoleate; metal salts consisting of naphthenic acid andmetals such as manganese, cobalt, nickel, zinc, chromium, magnesium,lead, iron, zirconium, calcium and aluminum.

The desirable amount of such a charge director dissolved is the carrierliquid consisting of said hydrocarbon is in the range of from 0.01 g to1 g per 1000 g of the carrier liquid.

Since these surface active agentsact as driers it may also be desirableto utilize them in the coating compositions of the present invention.

Pigments or coloring agents may be added, if desired, to either thecoating compositions or the electrostatic liquid toners of the presentinvention. Organic or inorganic pigments or coloring agents aresuitable. For example, carbon black, aniline black, cyanine black,spirit black, benzidine orange, benzidine yellow, methylene blue, alkaliblue, cyanine blue, phthalocyanine green etc. are applicable.

The proportion of the copolymer in the aliphatic hydrocarbon can varyover a wide range depending on whether it is to be usedfor coatingapplications or for toner applications. The amount of copolymer in thecoating composition can vary from about 0.1 to 70 percent by weight. Theamount of copolymer in the toner composition can vary from about 0.1 toabout 5 percent by weight.

Having described the basic concepts of the present invention,illustration will now be made by reference to the following exampleswhich are given by way of illustration, but not by way of limitation.

EXAMPLE I A non-aqueous polymeric dispersion is prepared according tothe prior art, that is by use of a prelent adhesion to the substrate(zinc oxide-binder syssynthesized polymeric dispersing agent. A typicaldispersing agent is the one described in US. Pat. No. 3,317,635 toDesmond Wilfrid John Osmond, assignor to Imperial Chemical Industries,column 12, example 3. The dispersing agent is a terpolymer 97/3/l.5 oflauryl methacrylate, alycidyl methacrylate and methacrylic acid, whichis prepared as a 30 percent solution in an aliphatic hydrocarbon boilingbetween ll0150C.

A mixture of of 1250 ml of lsopar G (isoparaffmic solvent with a boilingrange l58l76c) and 105 g of the solution of the polymeric dispersantdescribed above was heated to C in a vessel fitted with a stirrer, areflux condenser, and a thermometer. A mixture of 1.25 g of benzoylperoxide and 387.5 g of vinyl acetate is then added at once, whilemaintaining the temperature at 8590C. When polymerization startstakhours after appearance of cloudiness a mixture of 105 g of solutionof polymeric dispersant, 387.5 g of vinyl 4 acetate and 1.25 g ofbenzoyl peroxide is added over one hour period. The temperature of thedispersion is maintained at 85-90C for the next six hours.

Upon cooling, a 42 percent by weight, low viscosity, dispersion isformed which shows slight settling after a few days.

This dispersion can be used for coating purposes and can be diluted asdesired with some isoparaffinic solvent. It has good adhesion to varioussubstrates giving smooth clear coatings.

When diluted to a 1 percent by weight concentration with lsopar G, thedispersion can be used as a lithotoner for offset electrophotography.However, for best results, it is necessary to add 5-10 g of 50 percentsolution in mineral oil of zirconium octoate per liter of dispersion. Inthese conditions, toned litho-masters can be used to prepare offsetcopies of excellent quality. However, it was found that in some cases,after several months on the shelf some dispersions of this type hadatendency to settle out.

EXAMPLE II heated to C for twelve hours:

lsopar G ml Benzoyl peroxide 0.2 g Vinyl acetate 42.5 g

85/15 ratio Lauryl methacrylate 7.5 g

Once cooled, the resulting dispersion can be successfully used forcoating applications and produces hard clear coatings, with goodadhesion to various substrates such as paper, aluminum, glass, etc. Thelow viscosity 40 percent dispersion can be diluted with any hydrocarbontype solvent, such as lsopar G. One percent dispersions performed verywell as litho-toners in offset electrophotography. Used to tone ordevelop electrostatic images on zinc oxide coated papers, thelitho-toners of this invention showed exceltern), excellentoleophilicity and hydrophobicity, excellent resistance to etchingsolutions and abrasion and excellent stability even after several monthsof storage.

EXAMPLE III Example 11 was repeated except that an 80/20 ratio vinylacetate, lauryl methacrylate was used. An excellent non-aqueousdispersion could be prepared. It was diluted to 1 percent with Isopar Gand added 2.5 g of a 50 percent solution of zirconium octoate as acharge director, per liter of dispersion. It worked very well as alitho-toner, giving excellent offset copies, with no problem of settlingeven after six months of storage.

EXAMPLE IV Example II was repeated with 75/25 ratio of vinyl acetate tolauryl methacrylate. In this case too a-very stable polymeric dispersionwas formed with a low viscosity which could be used as well for coatingapplications as litho-toner applications.

EXAMPLE V Example II was repeated with a 50/50 ratio of vinyl acetateand lauryl methacrylate. At this level of lauryl methacrylate, aslightly more viscous dispersion is formed which can be successfullyused for coatings and adhesive applications.

EXAMPLE VI Example II was repeated with a 28/72 ratio of vinyl acetateand lauryl methacrylate. At this level of lauryl methacrylate, a hazysolution, of low viscosity is formed which can be used for adhesiveapplications, with excellent bonding characteristics to polyethylene oraluminum.

EXAMPLES VII, VIII, 1x

Example II was repeated except that lauryl methacrylate was replaced bystearyl methacrylate.

The following ratios of vinyl acetate and stearyl methacrylate weresuccessfully used to form stable non-aqueous dispersions: 90/10; 85/15;80/20.

These dispersions could be used for coating applications where thin,clear coatings adhering well to various substrates such as glass, paper,foil etc. are necessary.

The dispersions could be diluted at will with various hydrocarbonsolvents without any effect on the stability of the dispersion.

One percent by weight dispersions prepared by dilution of the 40 percentconcentrate with Isopar G were used as litho-toners in offsetelectrophotography. The quality of the copies generated was excellenteven without the addition of small amounts of charge directors.

Such litho-toners have excellent adhesion to the photoconductor coatedpaper, excellent oleophilicity and hydrophobicity, excellent resistanceto etching solutions, excellent stability and excellent charge holdingcharacteristics.

EXAMPLE X Example II was repeated except that lauryl methacrylate wasreplaced by 2-ethyl hexyl acrylate, with a 75/25 ratio of vinyl acetateto 2ethyl hexyl acrylate. A very stable, low viscosity dispersion wasformed which had application for coatings or adhesives purposes. Thisdispersion could be diluted without any loss of long-term stability.However, for litho-toner applications, this dispersion was not .asdesirable being somewhat more sensitive to etching solutions.

EXAMPLE XI EXAMPLE XII Using the same equipment as described in theexample II, the following compounds were mixed, stirred and heated at Cfor 5 hours:

Isopar G 300 ml. Benzoyl peroxide 0.4 g Methyl methacrylate 80 g 80/20'ratio Lauryl methacrylate 20 g However, a lot of polymer settled out ofthe dispersion while only 4-5 percent stayed in a stable dispersionform. Such a dispersion can be further diluted and used as alitho-toner. However, its adhesion to zinc oxide coated paper isinsufficient and unless used at high temperature, it is not as suitableas a litho-toner.

EXAMPLE XIII Example XII was repeated except that methyl metha crylatewas replaced by ethyl acrylate, with an 80/20 ethyl acrylatelaurylmethacrylate ratio. In this case the copolymer is practically soluble inthe solvent at a temperature above C. However, as the temperature goesdown, the copolymer becomes less and less soluble in the system forminga dispersion in a dispersion which could be advantageous for coatingpurposes.

Although specific ingredients ranges and proportions have been disclosedin the description of the preferred embodiments of the presentinvention, other well known and equivalent materials as listed above,where suitable, may be used with similar result. In addition, other wellknown additives may be incorporated in the compositions of the presentinvention to synergize, enhance, or otherwise modify the properties ofthe compositions. It will be appararent, therefore, that various changesand modifications can be made in the details of formulation, procedureand use without departing from the spirit of the present invention, saidinvention to be limited only as defined by the scope of the appendedclaims.

What is claimed is:

1. A composition of matter which is a stable, nonaqueous polymericdispersion prepared without the presence of a dispersing agent formaintaining the polymeric material as discrete particles, comprising: acopolymer of a low molecular weight unsaturated ester selected from thegroup consisting of vinyl acetate, vinyl propionate, methyl acrylate,ethyl acrylate, methyl methacrylate and ethyl methacrylate and at leastone copolymerizable long chain C to C aliphatic ethylenicallyunsaturated monomer selected from the group consisting of long chainacrylic, methacrylic and vinyl esters in a petroleum fraction organicliquid carrier selected from the group consisting of paraffinichydrocarbon and isoparaffinic hydrocarbon, wherein said low molecularweight unsaturated ester and said C to C aliphatic ethylenicallyunsaturated monomer are present in a ratio from about 95 to to about 50to 50 weight percent.

2. A composition of claim 1 wherein said low molecular weightunsaturated ester is vinyl acetate and said long chain C to C aliphaticethylenically unsaturated monomer is lauryl methacrylate.

3. A composition of claim 1 wherein said low molecular weightunsaturated ester is vinyl acetate and said 10 long chain C to Caliphatic ethylenically unsaturated monomer is stearyl methacrylate.

4. A method of preparing a stable non-aqueous co- 7 polymer dispersioncomposition which is prepared without the presence of a dispersing agentfor maintaining the polymeric material as discrete particles,comprising:

admixing a low molecular weight unsaturated ester selected from thegroup consisting of vinyl acetate,

methyl acrylate, ethyl acrylate, methyl methacrylate and ethylmethacrylate and a long chain C to C aliphatic ethylenically unsaturatedmonomer selected from the group consisting of long chain acrylic,methacrylic and vinyl esters in a petroleum fraction organic liquidcarrier selected from the group consisting of paraffinic hydrocarbon andisoparaffinic hydrocarbon in the ration of said low molecular weightmonomer to said long chain monomer of about 95 to 5 to about 50 to 50weight monomer is stearyl methacrylate.

2. A composition of claim 1 wherein said low molecular weightunsaturated ester is vinyl acetate and said long chain C6 to C20aliphatic ethylenically unsaturated monomer is lauryl methacrylate.
 3. Acomposition of claim 1 wherein said low molecular weight unsaturatedester is vinyl acetate and said long chain C6 to C20 aliphaticethylenically unsaturated monomer is stearyl methacrylate.
 4. A methodof preparing a stable non-aqueous copolymer dispersion composition whichis prepared without the presence of a dispersing agent for maintainingthe polymeric material as discrete particles, comprising: admixing a lowmolecular weight unsaturated ester selected from the group consisting ofvinyl acetate, methyl acrylate, ethyl acrylate, methyl methacrylate andethyl methacrylate and a long chain C6 to C20 aliphatic ethylenicallyunsaturated monomer selected from the group consisting of long chainacrylic, methacrylic and vinyl esters in a petroleum fraction organicliquid carrier selected from the group consisting of paraffinichydrocarbon and isoparaffinic hydrocarbon in the ration of said lowmolecular weight monomer to said long chain monomer of about 95 to 5 toabout 50 to 50 weight percent in the presence of a polymerizing agent,mixing and maintaining said admixture at a temperature of at least 60*C,and less than 130* C until substantial completion of copolymerization,and then allowing said admixture to cool.
 5. The method of claim 4 inwhich said low molecular weight unsaturated ester is vinyl acetate andsaid long chain C6 to C20 aliphatic ethylenically unsaturated monomer islauryl methacrylate.
 6. The method of claim 4 in which said lowmolecular weight unsaturated ester is vinyl acetate and said long chainC6 to C20 aliphatic ethylenically unsaturated monomer is stearylmethacrylate.